A conventional single blade wiper assembly comprises a primary yoke for attachment to a wiper arm, two secondary yokes pivotally attached to opposite ends of the primary yoke, and a separate tertiary yoke pivotally attached to one, usually the outermost one, of the two free ends of each secondary yoke. Claws for mounting a wiper blade are provided at the ends of the tertiary yokes, and at the ends of the secondary yokes not occupied by the tertiary blades. There is thus provided a flexible six point mounting for the wiper blade, which affords a reasonable degree of contact between the wiper blade and the windscreen, at least in calm conditions when the vehicle is stationary or travelling at comparatively slow speed.
Dual wiper blade assemblies are also know for mounting a pair of wiper blades. Typically a known dual wiper blade assembly comprises a primary yoke, one or two secondary yokes pivotally attached to each end of the primary yoke and a separate tertiary yoke articulated to one of the two ends of each secondary yoke. The free ends of each of the secondary and tertiary yokes are provided with claws for mounting a pair of generally parallel wiper blades.
A problem arises with known wiper blade assemblies, however, when the vehicle is travelling forwards, creating an upward and transverse air flow over the windscreen. The wiper blade assembly naturally tends to lift away from the windscreen on its downward stroke as air flow intervenes between the windscreen and the wiper. When the vehicle is travelling at speed, the problem is exacerbated.